Relationships between drug activity in NCI preclinical in vitro and in vivo models and early clinical trials.

An analysis of the activity of compounds tested in pre-clinical in vivo and in vitro assays by the National Cancer Institute's Developmental Therapeutics Program was performed. For 39 agents with both xenograft data and Phase II clinical trials results available, in vivo activity in a particular histology in a tumour model did not closely correlate with activity in the same human cancer histology, casting doubt on the correspondence of the pre-clinical models to clinical results. However, for compounds with in vivo activity in at least one-third of tested xenograft models, there was correlation with ultimate activity in at least some Phase II trials. Thus, an efficient means of predicting activity in vivo models remains desirable for compounds with anti-proliferative activity in vitro. For 564 compounds tested in the hollow fibre assay which were also tested against in vivo tumour models, the likelihood of finding xenograft activity in at least one-third of the in vivo models tested rose with increasing intraperitoneal hollow fibre activity, from 8% for all compounds tested to 20% in agents with evidence of response in more than 6 intraperitoneal fibres (P< 0.0001). Intraperitoneal hollow fibre activity was also found to be a better predictor of xenograft activity than either subcutaneous hollow fibre activity or intraperitoneal plus subcutaneous activity combined. Since hollow fibre activity was a useful indicator of potential in vivo response, correlates with hollow fibre activity were examined for 2304 compounds tested in both the NCI 60 cell line in vitro cancer drug screen and hollow fibre assay. A positive correlation was found for histologic selectivity between in vitro and hollow fibre responses. The most striking correlation was between potency in the 60 cell line screen and hollow fibre activity; 56% of compounds with mean 50% growth inhibition below 10(-7.5) M were active in more than 6 intraperitoneal fibres whereas only 4% of compounds with a potency of 10(-4) M achieved the same level of hollow fibre activity (P< 0.0001). Structural parameters of the drugs analysed included compound molecular weight and hydrogen-bonding factors, both of which were found to be predictive of hollow fibre activity.

Therapeutic and pharmacological studies of tetrachloro(d,l-trans)1,2-diaminocyclohexane platinum (IV) (tetraplatin), a new platinum analogue.

Tetrachloro(d,l-trans)1,2-diaminocyclohexane platinum (IV) (tetraplatin), a new platinum analogue, showed greater therapeutic efficacy after i.p. administration than either cis-dichlorodiammineplatinum (II) (cisplatin) or cis-diammine-1,1-cyclobutanedicarboxylate platinum (II) (carboplatin) in mice bearing i.p. implanted L1210 leukemia. At an optimal dose of 5.7 mg/kg/injection given as a single dose on days 1, 5, and 9, tetraplatin increased the median life span over controls by more than 566% with 5 of 8 long-term (50-day) survivors. In contrast, cisplatin at the same optimal dose increased survival by 186% with 2 of 8 long-term survivors, and carboplatin at an optimal dose of 75.6 mg/kg/injection increased survival by only 120% with no long-term survivors. Tetraplatin also was more effective than cisplatin when treatment was delayed until days 3, 7, and 11 after i.p. implant. A combination of tetraplatin and Adriamycin in mice bearing i.p. implanted L1210 leukemia produced more long-term survivors over a wider range of doses than could be achieved with either drug alone. Tetraplatin at 5.7 mg/kg/injection and Adriamycin at 3 mg/kg/injection on days 1, 5, and 9 increased survival by more than 566% with 8 of 8 50-day survivors. Using the same treatment schedule, combinations of tetraplatin with either cisplatin, carboplatin, daunomycin, or 5-fluorouracil did not produce therapeutic efficacy greater than that seen with tetraplatin alone. The in vitro cellular uptake of platinum by L1210 cells at 37 degrees C was about 4-fold higher after exposure to tetraplatin compared to cisplatin following a 2-h incubation at the two concentrations examined (2.5 and 5 micrograms/ml). Comparative pharmacological studies were performed in rats at a single dose of 3 mg/kg i.v. The t1/2 beta for total platinum in plasma was 29.10 h (7.47 h for unbound platinum) after the administration of tetraplatin and 23.70 h (13.09 h for unbound platinum) after cisplatin. By 48 h the urinary excretion of platinum after tetraplatin and cisplatin was 30.1% and 41.4%, respectively. Tissue distribution of platinum was similar after either complex. Thus, tetraplatin has similar pharmacological properties to cisplatin and like cisplatin is a candidate for combination chemotherapy. However, tetraplatin may be superior to cisplatin in some therapeutic situations based on its greater efficacy against selected tumors.

Relationship between in vitro tumor stem cell assay and in vivo antitumor activity using the P388 leukemia.

The relationship between in vitro tumor stem cell sensitivity and in vivo antitumor efficacy using 13 active antineoplastic agents was examined by means of the intraperitoneal P388 mouse leukemia system. The doses, which produced a 50% increase in life span after one, five and nine days of treatment, were all significantly correlated with the in vitro concentration producing a 70% reduction in colony formation during a seven-day continuous drug exposure. The five-day correlation was the best, followed by nine days and one day. Correlations were not improved by corrections for either in vitro drug stability or toxicity (LD50). The highly significant correlations observed in this simple retrospective analysis provide a basis for the development of more sophisticated models for the prediction of in vivo results from in vitro data.

Application of a human tumor colony-forming assay to new drug screening.

The applicability of a human tumor colony-forming assay to drug screening was investigated in terms of feasibility, validity, and potential for discovering new antitumor drugs. Feasibility was addressed in a pilot study during which basic methods, appropriate assay quality controls, and a standardized protocol for screening were developed. Considerable variability was noted in the availability and colony growth of different tumor types. The majority of the evaluable experiments utilized breast, colorectal, kidney, lung, melanoma, or ovarian tumors. For many tumor types, little evidence of growth was observed, or only rare specimens formed colonies. Colony-forming efficiencies ranged from 0.05 to 0.11% for the six most useful tumors listed above. A set of quality control measures was developed to address technical problems inherent in the assay. Testing of standard agents in the pilot study established that most of these agents could be detected as active. However, it also identified three assay limitations: compounds requiring systemic metabolic activation are inactive; medium constituents may block the activity of certain antimetabolites; and compounds without therapeutic efficacy may be positive in the assay. The assay categorized nontoxic clinically ineffective agents as true negatives with 97% accuracy. Of 79 compounds which were negative in the current National Cancer Institute prescreen (leukemia P388), 14 were active in the assay. Several demonstrated outstanding in vitro activity and are structurally unrelated to compounds already in development or in clinical trials. A subset of these active compounds were found to lack activity in a P388 in vitro colony-forming assay. This indication of differential cytotoxicity to human tumor cells makes this subset of compounds particularly interesting as antitumor drug leads. The demonstrated sensitivity to most standard agents, discrimination of nontoxic compounds, reproducibility of survival values within assays and between laboratories, and evidence of ability to identify active compounds which were negative in the in vivo prescreen suggest that the human tumor colony-forming assay may be a valuable tool for antitumor drug screening. However, because of technical limitations inherent in the current assay methodology, this must be confined to selected tumor types and limited to screening on a moderate scale.

The effectiveness of the anthracycline analog 4'-epidoxorubicin in the treatment of experimental tumors: a review.

The current report presents the data of the Division of Cancer Treatment of the National Cancer Institute (NCI) on the antitumor activity of the anthracycline antibiotic 4'-epidoxorubicin in experimental tumor systems. Direct comparisons are made with doxorubicin in individual experiments, and the data are related to those of earlier studies in the form of a review of experimental activity, in order to assess the relative activity of 4'-epidoxorubicin and doxorubicin. The experimental test models utilized by the NCI for these studies included the leukemias P388 and L1210, B-16 melanoma, Lewis lung carcinoma, the colon tumors 26 and 38, and the mammary tumors CD8F1 and C3H16/C. The human tumors growing in xenograft in athymic mice included the models LX-1 lung tumor, CX-1 colon tumor, and MX-1 mammary tumor. Additional comparisons were made with the tumor models Gross leukemia, sarcoma 180, MSV-induced sarcoma, MS-2 tumor, and a variety of human tumors growing in athymic mice, as well as with in vivo toxicologic and in vitro cytotoxicity models. Although for 4'-epidoxorubicin there is only a minimal alteration of the configuration of the doxorubicin molecule, quantitative comparison of 4'-epidoxorubicin and doxorubicin revealed not only similarities but also differences in biological activity. Both drugs showed activity against a broad spectrum of experimental tumors, with 4'-epidoxorubicin more effective against some tumors and equally effective against others. 4'-Epidoxorubicin evidenced less toxicity than doxorubicin in both acute and chronic toxicity studies with retention of therapeutic effectiveness and showed reduced cardiotoxicity. With 4'-epidoxorubicin there resulted a higher therapeutic index and therapeutic ratio, permitting the use of higher dosage and a greater margin of safety. The preclinical differences in therapeutic and toxicologic manifestations of 4'-epidoxorubicin, reflecting apparent alterations in pharmacologic properties and mode of action in comparison with doxorubicin, support the broad spectrum clinical trials of this already-demonstrated clinically active drug.

Potentials and drawbacks of the human tumor stem cell assay.

The human tumor stem cell assay (HTSCA) provides a means of performing drug sensitivity measurements on human tumor cells in primary culture. Results from such assays offer potential for improving cancer chemotherapy by identifying drugs useful for treatment of individual patients' tumors and through application to screening new compounds for antitumor activity. While existing data supports the potential of the assay in both areas, the assay also poses significant drawbacks. Many of these drawbacks relate to technical aspects of the assay and can be eliminated or reduced by further assay development. In this paper, we describe some of the technical drawbacks in detail and some approaches which have been successful in minimizing them. Continued advances in this area should make it possible to more fully realize the potential of the human tumor stem cell assay.

Calorie restriction: effect on growth of human tumors heterotransplanted in nude mice.

The presence of 4 human malignant tumors (1 breast, 1 lung, and 2 colon carcinomas) growing subcutaneously as heterotransplants in nude mice did not significantly affect the body weights of adult animals until the tumors reached very large dimensions (tumor wt greater than 15% of the body wt). However, a colon carcinoma (HT 29) induced a cessation of the natural rate of body weight increase when it grew in young adults (animals weighing approximately equal to 25 g which will gain 6 g or approximately equal to 25% body wt in 1 mo). Calorie restriction at all the levels tested (8, 6, 4, and 2 g/day/mouse) with standard pelletized mouse food produced both weight loss in the animals (with and without tumor) and a lowering of the growth rate of all the 4 tumors tested growing at a subcutaneous site and/or under the kidney capsule. Each tumor responded differently to the calorie restriction. The 4 tumors tested grew equally in both male and female nude mice. Young animals weighing 20 g inoculated with a fifth tumor (MeWo melanoma) exhibited tumor growth inhibition proportional to restriction of calorie intake. Their survival, however, did not improve.

Usefulness and limitations of murine tumor models for the identification of new antitumor agents.

Murine tumor systems that have been employed in the identification of most of the known antitumor agents are reviewed and their usefulness and limitations in the identification of new antitumor agents is discussed. A new antitumor screening program has been initiated by the Division of Cancer Treatment, National Cancer Institute which employs human tumors growing in athymic mice. The questions addressed using this screen and representative data are presented.

Adequacies and inadequacies in assessing murine toxicity data with antineoplastic agents.

Previous retrospective analyses have suggested a very positive correlation in toxic doses of antineoplastic agents between mice and humans. Additional toxicological information has now been accumulated and reveals a noticeable variability in the existing data base. Nevertheless, it is likely that mouse toxicological studies will become a principal determinant for estimating initial doses to be used in humans. Recognition of the factors responsible for differences in determinations of toxic dose levels in mice will enhance the proper utilization of this approach.